Surface Enhanced Raman Scattering (SERS) was first demonstrated in 1977 (Jeanmaire et al., J Electroanal Chem 84: 1 (1977)). SERS significantly increased the magnitude of a Raman scattering signal by functionalizing a molecule onto a rough metal surface (Haynes et al., Anal Chem 77: 338A (2005)). It also has been reported that using metal nanoparticles as substrates in SERS provided for 1014 increased signal (Kniepp et al., Phys Rev Lett 78: 1667 (1997) and Nie et al., Science 275: 1102 (1997)). This advancement made single molecule detection possible and showed promise in biological detection applications (Cao et al., Science 297: 1536 (2002); Cao et al., J Am Chem Soc 125: 14676 (2003); and Doering et al., Anal Chem 75: 6171 (2003)). In the investigation of single molecule and single particle SERS, researchers have found that some particles demonstrated a much higher enhancement, which were labeled “hot spots.” Although researchers in the field reported the identification of various Raman hot spots, no work has reported a systematic study of Raman hot spots.
Substrates previously used for SERS applications include roughened metal surfaces, such as those reported in U.S. Pat. No. 6,970,239. No control over the roughened surface or of the porous characteristics of the metal surface was disclosed. Because the porosity of the metal surface is theorized to be a major factor in the enhancement of Raman scattering, control over the characteristics of the metal surface is needed both to better understand the role porosity plays in the enhancement and to provide optimum surface characteristics for SERS detection of analytes. Optimization may provide an ability to detect small, even single molecule, amounts of an analyte of interest.